Electrochromic assembly based on poly(3,4-ethylenedioxythiophene) derivatives and a UV-stabilized gel electrolyte

ABSTRACT

UV-stabilized electrochromic assemblies having a layer structure, characterized in that one layer contains an electrically conductive, electrochromic polydioxythiophene and a further layer contains an inorganic ion-storage compound based on metal oxides or a mixture of such ion-storage compounds, where the gel electrolyte is chemically crosslinked and contains chemically bound UV absorbers which cannot migrate as UV protection.

BACKGROUND OF THE INVENTION

The present invention relates to electrochromic assemblies containingUV-stabilized crosslinked gel electrolytes and having controllable lighttransmittance, their production and their use.

The transparency of windows of vehicles in respect of electromagneticradiation has hitherto not been able to be regulated. Phototropicglasses have hitherto been used only as glass in spectacles and haveonly a relatively small change in the transmission. Windows of buildingshave hitherto been darkened by means of curtains, shutters, rollerblinds or other movable mechanical elements. Electrochromic devices canthus be employed in a wide variety of ways. A brief overview of examplesis as follows:

1. Vehicle glazing (windows or sunroofs of automobiles)

An electrochromic device is suitable as protection against sun ordazzling in motor vehicles. Front, side and rear windows or glass roofscan be included. The degree of darkening can be matched zone-wise andsteplessly to the needs of the driver depending on the position of thesun and the immediate driving situation. Integration into acomputer-controlled regulating system is possible. A combination of anactive element with a laminated glass unit is likewise possible, forexample application of a film system to the safety glass.

The transmittance of the windows can be controlled manually orautomatically, which can be used for effective protection againstdazzling during night driving, automatic adjustment of the level ofbrightness on driving into and out of tunnels and multistorey car parksand for protection against forced entry and theft when the vehicle isparked by preventing a view into the interior of the vehicle. Excessiveheating of the interior in summer, particularly when the vehicle isparked can be prevented (cf. EP-A 0 272 428).

2. Glazing of buildings (electrochromic window)

In buildings, electrochromic assemblies are suitable for darkening sidewindows and skylights of buildings, living areas, workrooms orgreenhouses as controllable sun protection (visible spectral region) andheat protection (IR region) and also for protection of the eyes (visiblespectral region). For protection against break-ins, glazing of bankcounters or shop windows can be darkened at the press of a button. Glassdoors can automatically be made visible on the approach of persons inorder to avoid injury. The ability to generate virtually all coloursalso makes it possible to incorporate the glazing architecturally intothe facade of a building. The energy consumption for controlling thetransparency of a large area of window is low, particularly when thememory effect of the system can be exploited and energy is only consumedin the switching phase. A combination with heat-protection glazing (Kglass) is very well suited to achieving dynamic control of the sunlightshining through a window ("smart window"). Thus, an electrochromicsystem can contribute to regulating and limiting the energy required forair conditioning of buildings.

The power supply to the system can also be achieved by means of solarmodules. A light-sensitive sensor can determine the intensity of thesunlight and thus control the light transmittance.

3. Display elements

The ability to produce attractive colours and display any desiredcontours, e.g. letters, numbers, signs and symbols (able to be producedby appropriate structuring techniques) on a large area providesadvertizing with an interesting medium. Decorative and informativeeffects are readily possible.

Apart from the possibility of locating the system between panes ofglass, there is also the alternative of using two or even only onetransparent plastic film as support. This makes it possible to achieveplacard-like advertizing materials with changeable information.

Electrochromic devices can be used for small display elements such asfaces of watches and clocks or measuring instruments, displays for awide variety of applications and for large display elements such astraffic signs, advertizing columns, information displays at railwaystations and airports or for providing parking directions. Use asvariable delineation system (marking of boundaries etc. on playingareas) in sports halls is likewise possible.

They can be used wherever information is to be made visible.

4. Optics

In optics, electrochromic systems can be used either in combination withglasses, lenses and filters of other optical instruments as well as soleactive components. Use as fade-over protection for optical detectionsystems is likewise possible. The system is likewise suitable as acontrollable filter system in photographic processes.

5. Mirrors

An electrochromic device can also be used as a dimmable mirror, e.g. inan automobile as external or rear-view mirror, which can be darkened byapplication of an electric potential and thus prevents dazzling by theheadlights of other vehicles (cf., for example, U.S. Pat. No. 3,280,701,U.S. Pat. No. 4,902,108 (Gentex), EP-A 0 435 689, U.S. Pat. No.5,140,455). A disadvantage of systems of the prior art (solutionsystems) is the colour in homogeneity after prolonged operation(segregation), particularly in the case of large mirrors (e.g. mirrorsof goods vehicles). Increasing the viscosity of the solution system byaddition of polymeric thickeners has been described (e.g. U.S. Pat. No.4,902,108).

6. EMI shielding

An electrochromic device can also be used as a variable filter elementfor modulating electromagnetic radiation in certain wavelength ranges.

Electrochromic devices usually comprise a pair of glass or plasticplates of which one is mirrored in the case of a mirror. One side ofeach of these plates is coated with a translucent electricallyconductive layer, e.g. indium-tin oxide (ITO). These plates are used toconstruct a cell by fixing them with their conductively coated sidesfacing one another. The cell between the plates contains theelectrochromic system and is closed tightly. The two plates can beseparably connected to a power source and controlled via the conductivelayer.

In the electrochromic solution systems known from the above-cited priorart, pairs of redox substances which after reduction or oxidation formcoloured, positively or negatively charged free radicals which arechemically reactive are present in a solvent.

Examples are the viologen systems which have been known for a long time.

As the pair of redox substances, use is made of one reducible and oneoxidizable substance. Both are colourless or have only a slight colour.Under the action of an electric potential, one substance is reduced andthe other is oxidized, with at least one becoming coloured. After thepotential is switched off, the two original redox substances are formedagain, with decolouration or lightening of the colour occurring.

It is known from U.S. Pat. No. 4,902,108 that pairs of redox substancesin which the reducible substance has at least two chemically reversiblereduction waves in the cyclic voltammogram and the oxidizable substancecorrespondingly has at least two chemically reversible oxidation wavesare suitable. Systems of this type are suitable mainly for dimmable rearview mirrors of automobiles. Since these are solution systems, they arenormally not suitable for use in electrochromic windows.

Also known are systems in which the actual electrochromic redox pair isdispersed in a polymer matrix (see, for example, WO-A 96/03475). Theundesirable effect of segregation is suppressed in this way.

Combinations of inorganic electrochromic components such as WO₃, NiO orIrO₂ are likewise known and are possibilities as components in anelectrochromic window (see, for example, U.S. Pat. No. 5,657,149,Electronique International No. 276, 16 (1997)).

These inorganic electrochromic components can be applied to theconductive substrate only by vapour deposition, sputtering or by asol-gel technique. As a result, systems of this type are very expensiveto produce. Efforts to replace one inorganic component by an organicpolymer component have resulted in, for example, electrochromic systemsbased on the electrically conductive polymer polyaniline (PANI) and WO₃as complementary electrochromic materials becoming known (see, forexample, B. P. Jelle, G. Hagen, J. Electrochem. Soc., Vol. 140, No. 12,3560 (1993)). An attempt has also been made to use systems without aninorganic component in which the ITO or SnO₂ layer (counterelectrode) issupposed to serve as complementary electrochromic component tosubstituted poly(3,4-alkylenedioxythiophenes) (U.S. Pat. No. 5,187,608).

However, it is found that such electrochromic assemblies are not able toensure a sufficient number of switching cycles without a changeoccurring in the properties of the device. In addition, suchelectrochromic assemblies are generally sensitive to light, inparticular UV light. For this reason, electrochromic assembliescontaining UV stabilizers are also known, for example from U.S. Pat. No.5,280,380.

SUMMARY OF THE INVENTION

The present invention provides a UV-stabilized electrochromic assemblyhaving a layer structure and containing at least one UV absorber,characterized in that one layer is an electrically conductive,electrochromic polydioxythiophene and a further layer is an ion-storagecompound or a mixture of ion-storage compounds of the formulae (I) to(XXI)

    ______________________________________                                        Me.sup.1 O.sub.2      (I)                                                     Me.sup.2.sub.2 O.sub.5                                                                              (II)                                                    Li.sub.x Me.sup.1 O.sub.2                                                                           (III)                                                   Li.sub.x Me.sup.2.sub.2 O.sub.5                                                                     (IV)                                                    Li.sub.x Me.sup.1 O.sub.2+x/2                                                                       (V)                                                     Li.sub.x Me.sup.2.sub.2 O.sub.5+x/2                                                                 (VI)                                                    Me.sup.3 O            (VII)                                                   Me.sup.3 O.sub.x      (VIII)                                                  M.sub.x Me.sup.3 O    (IX)                                                    M.sub.x Me.sup.3 O.sub.2                                                                            (X)                                                     M.sub.x Me.sup.3 O.sub.y                                                                            (XI)                                                    Me.sup.4 O.sub.3      (XII)                                                   M.sub.x Me.sup.4 O.sub.3                                                                            (XIII)                                                  M.sub.x Me.sup.4.sub.(1-x) Me.sup.4.sub.x O.sub.3                                                   (XIV)                                                   Me.sup.3 (OH).sub.2   (XV)                                                    Me.sup.3 O(OH)        (XVI)                                                   MMe.sup.3 O.sub.2     (XVII)                                                  Me.sup.3 O.sub.2      (XVIII)                                                 Me.sup.3.sub.2 O.sub.3                                                                              (XIX)                                                   Me.sup.3.sub.2 O.sub.3.H.sub.2 O                                                                    (XX)                                                    LiMe.sup.5 O.sub.3    (XXI)                                                   ______________________________________                                    

where

Me¹ and Me² each represent a metal transition group III, IV or V of theMendeleev Periodic Table,

Me³ and Me⁴ each represent a metal of transition group VI or VIII of thePeriodic Table,

Me⁵ represents a metal of transition group V of the Mendeleev PeriodicTable,

x represents a number from 0.001 to 5,

y represents a number from 0.001 to 5,

M preferably represents a metal of main group I of the Periodic Table ora proton,

Me¹ preferably represents zirconium, cerium or titanium,

Me² preferably represents vanadium or niobium,

Me³ preferably represents nickel or iridium,

Me⁴ preferably represents molybdenum or tungsten,

Me⁵ preferably represents vanadium, niobium or tantalum.

Very particular preference is given to using the following ion-storagelayers:

    ______________________________________                                        V.sub.2 O.sub.5      NiO                                                      Li.sub.x V.sub.2 O.sub.5                                                                           NiO.sub.2                                                Li.sub.x V.sub.2 O.sub.5+x/2                                                                       Ni(OH).sub.2                                             CeO.sub.2            NiO(OH)                                                  Li.sub.x CeO.sub.2   LiNiO.sub.2                                              Li.sub.x CeO.sub.2+x/2                                                                             Ni.sub.2 O.sub.3                                         Nb.sub.2 O.sub.5     Ni.sub.2 O.sub.3.H.sub.2 O                               Li.sub.x Nb.sub.2 O.sub.5                                                                          Li.sub.x NiO                                             Li.sub.x Nb.sub.2 O.sub.5+x/2                                                                      WO.sub.3                                                 LiNbO.sub.3.                                                                  ______________________________________                                    

The ion-storage layer can also be a mixture of at least two of thecompounds (I) to (XXI).

Particular preference is given to using the following mixtures:

    TiO.sub.2 --CeO.sub.2

    CeO.sub.2 --V.sub.2 O.sub.5

    TiO.sub.2 --V.sub.2 O.sub.5

    Li.sub.x CeO.sub.2 --Li.sub.x V.sub.2 O.sub.5

    Li.sub.x TiO.sub.2 --Li.sub.x V.sub.2 O.sub.5

    Li.sub.x TiO.sub.2 --Li.sub.x Ceo.sub.2

    V.sub.2 O.sub.5 --Nb.sub.2 O.sub.5

    Li.sub.x V.sub.2 O.sub.5 --Li.sub.x Nb.sub.2 O.sub.5

    NiO--CeO.sub.2

    NiO--TiO.sub.2

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the schematic structure of electrochromic assembliesaccording to the invention.

FIG. 2 illustrates the effect of electric current on the color of aUV-stabilized cell prepared according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

The ion-storage layer in the assembly of the invention thus comprises ametal oxide compound or a mixture of metal oxides. The ion-storagelayers can include an Li salt when they are produced or else can beloaded electrochemically with Li ions afterwards.

The compounds of the formulae (I) to (XXI) are generally knowncompounds, are commercially available or can be prepared by generallyknown methods of inorganic chemistry (cf., for example,Hollemann-Wiberg, Lehrbuch der organischen Chemie, 71st-80th edition,Walter de Gruyter & Co., Berlin 1971, pages 779-781; Rompp ChemieLexikon; Chemical Abstract 1313-96-8 or P. M. S. Monk, R. J. Mortimer,D. R. Rosseinsky; Electrochromism, VCH-Verlag, Weinheim 1995.

Nickel oxides and hydrated nickel oxide are described in GmelinsHandbuch der anorganischen Chemie, Verlag Chemie, 8^(th) edition 1996 orN. Ozer, C. H. Lampert, Solar Energy Materials and Solar Cells 39(1995), 367 for the example LiNbO₃.

The electrochromic assembly of the invention thus contains at least oneinorganic ion-storage layer. This can be applied either by means of asol-gel process or by vapour deposition/sputtering or electrochemicallyto an electrically conductive substrate which may be provided with ametal grid to improve the conductivity. The layer can also comprisenanosize particles which can be applied by means of a casting technique.

The polydioxythiophenes are cationically charged and comprise structuralunits of the formula (XXII) ##STR1## where A¹ and A² each represent,independently of one another, substituted or unsubstituted (C₁-C₄)-alkyl or together form substituted or unsubstituted (C₁-C₄)-alkylene, and

n represents an integer from 2 to 10,000, preferably from 5 to 5000,

in the presence of polyanions.

Preferred cationic polydioxythiophenes comprise structural units of theforrnula (XXIIa) or (XXIIb) ##STR2## where R₁ and R₂ represent,independently of one another, hydrogen, substituted or unsubstituted (C₁-C₁₈)-alkyl, preferably (C₁ -C₁₀)-, in particular (C₁ -C₆)-alkyl, (C₂-C₁₂)-alkenyl, preferably (C₂ -C₈)-alkenyl, (C₃ -C₇)-cycloalkyl,preferably cyclopentyl or cyclohexyl, (C₇ -C₁₅)-aralkyl, preferablyphenyl-(C₁ -C₄)-alkyl, (C₆ -C₁₀)-aryl, preferably phenyl or naphthyl,(C₁ -C ₁₈)-alkyloxy, preferably (C₁ -C₁₀)-alkyloxy, for example methoxy,ethoxy, n- or iso-propoxy, or (C₂ -C₁₈)-alkyloxy ester and

R₃, R₄ represent, independently of one another, hydrogen, but not bothat the same time, or (C₁ -C₁₈)-alkyl, preferably (C₁ -C₁₀)-, inparticular (C₁ -C₆)-alkyl, (C₂ -C₁₂)-alkenyl, preferably (C₂-C₈)-alkenyl, (C₃ -C₇)-cycloalkyl, preferably cyclopentyl or cyclohexyl,(C₇ -C₁₅)-aralkyl, preferably phenyl-(C₁ -C₄)-alkyl, (C₆ -C₁₀)-aryl,preferably phenyl or naphthyl, (C₁ -C₁₈)-alkyloxy, preferably (C₁-C₁₀)-alkyloxy, for example methoxy, ethoxy, n- or iso-propoxy, or (C₂-C₁₈)-alkyloxy ester each of which are substituted by at least onesulphonate group,

n represents a number from 2 to 10,000, preferably from 5 to 5000.

Very particularly preferably, the electrochromic assembly of theinvention contains at least one electrically conductive, electrochrorniccationic or uncharged polydioxythiophene of the formulae (XXIIa-1)and/or (XXII b-1) ##STR3## where R₃ is as defined above,

n represents an integer from 2 to 10,000, preferably from 5 to 5000.

The polyanions are the anions of polymeric carboxylic acids such aspolyacrylic acids, polymethacrylic acids or polymaleic acids or ofpolymeric sulphonic acids such as polystyrenesulphonic acids andpolyvinylsulphonic acids. These polycarboxylic and polysulphonic acidscan also be copolymers of vinylcarboxylic and vinylsulphonic acids withother polymerizable monomers such as acrylic esters and styrene.

The anion of polystyrenesulphonic acid is particularly preferred ascounterion.

The molecular weight of the polyacids providing the polyanions ispreferably from 1000 to 2,000,000, particularly preferably from 2000 to500,000. The polyacids or their alkali metal salts are commerciallyavailable, e.g. polystyrenesulphonic acids and polyacrylic acids, orelse can be prepared by known methods (see, for example, Houben-Weyl,Methoden der organischen Chemie, vol. E 20 Makromolekulare Stoffe, part2, (1987), p. 1141 ff.).

In place of the free polyacids required for the formation of dispersionsof polydioxythiophenes and polyanions, it is also possible to usemixtures of alkali metal salts of the polyacids and correspondingamounts of monoacids.

In the case of the formula (XXIIb-1), the polydioxythiophenes bearpositive and negative charges in the structural unit. The preparation ofthe polydioxythiophenes is described, for example, in EP-A 0 440 957(=U.S. Pat. No. 5,300,575).

The polydioxythiophenes are obtained by oxidative polymerization. As aresult they acquire positive charges which are not shown in theformulae, since their number and position cannot be unambiguouslydetermined.

The present invention accordingly provides a light-stabilizedelectrochromic assembly containing electrically conductivepoly(3,4-ethylenedioxythiophene) derivatives as cathodically colouringelectrochromic polymers and, in addition, suitable ion-storage layersfor Li ions. A gel electrolyte comprising a crosslinked polymer, an Lisalt and a certain amount of a solvent is located between theelectrochromic polymer layer and the ion-storage layer. The schematicstructure is shown in FIG. 1, principle I).

Legend for FIG. 1:

1,2: substrate

3,4: electrically conductive coating, of which one can act as a mirror

5: electrochromic polymer, e.g. PEDT/PSS

6: ion-storage layer

7: gel electrolyte (crosslinked or uncrosslinked)

8,9: fine metal grid (optional)

The assembly of the invention additionally contains at least one UVabsorber or a light stabilizer selected from the group consisting of

benzophenones

benzotriazoles

organonickel compounds

salicylic esters

cinnamic esters

benzylidene malonates

benzoic esters

oxalanilides

stearically hindered amines

polymeric stearically hindered amines,

with the light stabilizer or a mixture of a plurality of lightstabilizers being chemically incorporated into the network of achemically crosslinked polymeric gel electrolyte (see layer 7 in FIG. 1)by means of acrylate groups, methacrylate groups, allyl groups, vinylgroups, hydroxy groups or carboxy groups.

UV absorbers or light stabilizers are generally known (see, for example,Modern Plastics Encyclopedia, McGraw-Hill Inc., New York 1982) and arecommercially available under various trade names (e.g. ®Chimassorb,®Uvinul, ®Irgastab, etc) from various suppliers (e.g. Ciba-Geigy, BASF,Clariant, etc).

UV absorbers having reactive groups are likewise known and can beobtained, for example, from Polysciences Europa GmbH, Eppelheim, or fromAldrich, Germany. The advantage of chemically bound UV absorbers is thatthey can no longer migrate in the matrix.

The light stabilizers are preferably incorporated photochemically orthermally by means of

acrylate groups

methacrylate groups

allyl groups

vinyl groups

hydroxy or carboxy groups

into a matrix which serves as gel electrolyte in an electrochromicassembly.

Examples which may be mentioned here are:

.) From the group of benzophenones/acetophenones: ##STR4##

Essential constituents of the light-stabilized electrochromic layerstructure of the invention are UV absorbers. They are used in an amountin the range from 0.01 to 10% by height, preferably from 0.04 to 5% byweight in the gel electrolyte. The UV absorbers present in the layerstructure of the invention are known in principle or can be prepared bya method analogous to the preparation of the known UV absorbers.Preferred UV absorbers are benzophenones and benzotriazoles. These arecommercially available.

The effect of the UV absorbers was measured in electrochromic assembliesas described further below. The illumination apparatus used was theXenotest 150 S from Heraeus. The power was 1,570 W/m² in the "outdoorsunlight" configuration.

The electrochromic polymer layer is transparent in the doped state. Thiscan be converted into a coloured form by uptake of electrons (reduction)at the cathode with an increase in the absorbance in the visible regionof the spectrum. The oxidation which occurs on the opposite side (anode)is associated with an exchange reaction of the ion-storage layer with Liions. However, this reaction barely contributes to the generation ofcolour, so that it does not interfere.

The present invention accordingly provides a light-stabilizedelectrochromic solid-state system containing at least one redox-activeelectrically conductive polymer selected from the group consisting ofpoly(3,4-ethylenedioxythiophene) derivatives which can, to enable themto be processed from solution, have been admixed withpolystyrenesulphonate or bear a solubilizing sulphonate group in a sidechain, and at least one light stabilizer. This polymer layer ispreferably applied from aqueous solution, in which case the solvent isevaporated to leave the solid, dry polymer film on the substrate.However, it should also be possible to apply it by screen printing. Assubstrates, preference is given to using an electrically conductive,transparent glass or film system where a layer of indium-tin oxide(ITO), fluorine-doped tin oxide (FTO, K -Glas), undoped tin oxide or alayer of finely divided silver serves as electrode. It is also possiblefor one electrode side to consist of a metal layer (e.g. Al, Cu, Pd)which is no longer transparent (for use in a mirror). The gelelectrolyte contains at least one polymer (e.g. polyethylene oxide,PMMA), at least one Li salt (e.g. Li triflate, Li perchlorate), at leastone solvent (e.g. propylene carbonate) and at least one lightstabilizer.

The present invention provides for the use of the electrochromicassembly of the invention in the glazing of buildings or architecturalglazing or sunroof in vehicles and also as display element, aselectrochromic mirror (e.g. automatically dimmable rear view mirror inautomobiles) and in various optical elements.

For use as a mirror, one of the two electrodes can consist of avapour-deposited or electrochemically deposited metal layer, e.g.aluminum, silver, copper, platinum, palladium or rhodium.

The present invention also provides a light-stabilized electrochromicsystem in which the colour-producing electrochromic polymer compoundfunctions simultaneously as its own electrode, as a result of which onlya conductive coating of ITO, fluorine-doped tin oxide or a metal isnecessary. (see FIG. 1, principle II)).

Legend for FIG. 1, principle II:

1,2: substrate

4: electrically conductive coating which can also act as a mirror

5: electrochromic polymer

6: ion-storage layer

7: gel electrolyte (crosslinked or uncrosslinked)

8,9: fine metal grid (optional)

The light-stabilized electrochromic assembly of the invention isparticularly notable for the fact that a combination with aheat-protection glass (commercially available for architectural glazingpurposes) explicitly as a positive feature of the assembly is possiblefor saving energy in the case of brightly sunlit rooms and can also beexposed to intense, direct sunlight. Further explicit electrodes ofanother material are thus unnecessary, since the heat-protection layerlimits the transmission of IR radiation and at the same time, due to itselectric conductivity, assumes the electrode function in theelectrochromic assembly.

The light-stabilized electrochromic assembly of the invention is alsonotable for the fact that the electrochromic layer can also absorb IRradiation in certain ranges and can thus limit the passage of heatthrough the pane.

The light-stabilized electrochromic layer structure of the invention issuitable as a constituent of an electrochromic device. In anelectrochromic device, the light-stabilized electrochromic assembly ofthe invention serves as a medium having variable transmission, i.e. thelight transmittance of the system alters under the action of an electricpotential as a result of it changing from a colourless to a colouredstate. The present invention therefore also provides electrochromicdevices containing a light-stabilized electrochromic assembly accordingto the invention. Applications of this electrochromic device are inarchitectural glazing and in vehicles, e.g. as window, automobilesunroof, rear view mirror in an automobile, display or as an opticalelement or as constituent of information display units such asinstrument displays in vehicles of all types. It can likewise be used asa window in a greenhouse.

If the electrochromic device is a electrochromic display device, atleast one of the two conductive layers or both is/are divided intoelectrically separate segments which are individually connected to apower source.

However, it is also possible for only one of the two plates to have aconductive coating and to be divided into segments. The segments can beseparated, for example, by mechanical removal of the conductive layer,e.g. by scoring, scratching, scraping or milling, or by chemical means,for example by etching using, for example, a hydrochloric acid solutionof FeCl₂ or SnCl₂. The location of this removal of the conductive layercan be controlled by means of masks, e.g. masks of photoresist. However,the electrically separate segments can also be produced by targeted,e.g. by means of masks, application, e.g. by sputtering or printing, ofthe conductive layer. The segments are connected to a power source bymeans of, for example, fine strips of conductive material so that thesegment is electrically connected to a contact at the edge of theelectrochromic device. These fine contact strips can consist of the samematerial as the conductive layer itself and can be produced togetherwith it as described above, for example when it is divided intosegments. However, they can also, e.g. to improve the conductivity,consist of another material such as fine metallic conductors, forexample of copper or silver. A combination of metallic material and thematerial of the conductive coating is also possible. The metallicconductors can, for example, either be applied in fine wire form, e.g.adhesively bonded on, or be printed on. All these above-describedtechniques are generally known from the production of liquid-crystaldisplays (LCDs).

In the case of displays, the displays produced according to theinvention can be viewed in transmitted light or in reflected light bymeans of mirroring.

If the electrochromic device is an electrochromic window, a fine metalgrid can be vapour-deposited on one or both electrodes. This improvesthe surface conductivity of the substrates and is advantageous in thecase of large areas in order to achieve uniform colouring.

The light-stabilized electrochromic assembly of the invention preferablycontains at least one transparent electrically conductive coatingcomprising indium-tin oxide (In₂ O₃ :SnO₂ (ITO)), tin oxide (SnO₂),fluorine-doped tin oxide (SnO₂ :F; FTO or "K-glass", "heat-protectionglass"), antimony-doped tin oxide, antimony-doped tin oxide,aluminium-doped zinc oxide or a transparent metal film which issufficiently thin, e.g. silver coating (heat-protection glass, e.g.®PLANITHERM from Saint-Gobain), on a substrate (glass or plastic).

Other conductive polymers such as substituted or unsubstitutedpolythienyls, polypyrroles, polyanilines, polyactetylene orpolythiophenes can also be used.

In the light-stabilized assembly of the invention, the actualelectrochromic polymer is advantageously also used as its own conductiveelectrode material in place of one of the abovementioned conductivecoatings.

Very particular preference is given to using indium-tin oxide (In.sub.O₃ :SnO₂ (ITO)), tin oxide (SnO₂), fluorine-doped tin oxide (SnO₂ : F;FTO, "K-glass", "heat-protection glass") or a transparent silver coatingwhich is sufficiently thin (heat-protection glass or heat-protectionfilm).

If one of the plates is mirrored, this conductive layer can also beutilized. Particular preference is here given to using silver, aluminum,copper, platinum, palladium and rhodium.

The light-stabilized electrochromic assembly of the invention preferablycontains a transparent gel electrolyte comprising the followingcomponents:

polymer (crosslinked)

Li salt

solvent or solvent mixture

light stabilizer or mixture of a plurality of light stabilizers whichare chemically bound to the matrix.

Particular preference is given to using photocrosslinkable polyethersand polyethylene oxides as the polymer matrix.

Particular preference is given to photocrosslinkable polymer systemsbased on acrylates, e.g. polyethylene glycol 400 diacrylate,polyethylene glycol 400 dimethacrylate, polyethylene glycol 600diacrylate, polyethylene glycol 600 dimethacrylate, polyethylene glycolmethacrylate, tripropylene glycol diacrylate, tripropylene glycolmonomethyl ether acrylate, trimethylolpropane triacrylate, ethyleneglycol dimethacrylate, hydroxyethyl methacrylate (HEMA), hexanedioldiacrylate, dianol diacrylate, tetraethylene glycol diacrylate,pentaerythritol triacrylate, pentaerythritol tetracrylate, butylmethacrylate and also the acrylates Roskydal® UAVPLS 2258 and Roskydal®UALPV 94/800 from Bayer AG. The photocrosslinkable polymer systemsshould still be able to be cured in the presence of the solvent used andthe Li salt with the aid of light activation by means of a customaryphotoinitiator such as Darocure 1173, 1116 or Irgacure 184 (E. MerckKGaA,

Darmstadt) even between thick glass plates which are provided with atransparent electrically conductive coating. Illumination is carried outafter filling the cell by irradiation with a suitable lamp (e.g. UVlamps such as Hg or Xe lamps). Curing of polymer systems by electronbeam curing is likewise possible for the systems mentioned.

Very particular preference is also given to modified siloxanes derivedfrom, for example, gamma-glycidylpropyltrimethoxysilane. Variantsmodified by means of propylene oxide, for example, are also possible.

Apart from the UV absorbers, the gel electrolytes can also containorganic and/or inorganic fillers or additives. Here, the customaryadditives such as heat stabilizers, optical brighteners, flameretardants, flow improvers, fire retardants, dyes, pigments, fillers orreinforcing materials, finely divided minerals, fibres, chalk, quartzflour, glass, aluminum oxide, aluminum chloride and carbon fibres can beadded in customary amounts. The function of a spacer can be performed,for example, by glass spheres, polymer particles, silica gel or sandgrains having a defined size, should this be necessary.

Preferred Li salts are LiClO₄, LiCF₃ SO₃, LiN(SO₂ CF₃)₂, LiCl and LiPF₆.

Very particular preference is here given to LiClO₄, LiCF₃ SO₃ andLiN(SO₂ CF₃)₂.

Particularly preferred solvents are propylene carbonate, ethylenecarbonate, acetonitrile and γ-butyrolactone and also mixtures thereof.

Very particular preference is given to using propylene carbonate andethylene carbonate.

Substrates used in the light-stabilized electrochromic assembly of theinvention are glass or various types of plastic.

Preference is given generally to transparent substrates of any type.

Apart from glass, specifically heat-protection glass when used aselectrochromic window (in thicknesses of 10 μm in the case of "flexibleglass, thin glass" to 3 cm), particularly preferred materials arepolyesters (e.g. polyethylene terephthalate (PET) or polyethylenenaphthalate (PEN)), various types of polycarbonate (e.g. ®Makrolon,APEC-HT), polysulphones, polyimides and polycycloolefins. The polymericsubstrate can be used as flexible film or as a thick plate. Thesubstrate can also be curved so that the assembly matches the shape ofthe material underneath. A flexible plastic substrate can also, afterconstruction of the overall electrochromic system, be laminated oradhesively bonded onto various materials, e.g. curved glass.

The plastic substrates can additionally be provided with barrier layersagainst water and oxygen.

Preference is here given to TiO_(x), SiO_(x) on polyester, e.g.polyethylene terephthalate, DuPont, (cf. packaging films) or fluorinatedpolymers and possible combinations thereof and also barrier layers basedon inorganic-organic hybrid systems.

The light-stabilized electrochromic assembly of the invention can, whenconfigured as a flexible film system, be laminated or adhesively bondedas complete electrochromic composite system onto the safety glass ofautomobiles. In addition, it can be integrated into the hollow space ofa double glazing system in buildings.

The control mechanism of the electrochromic assembly is based on thereversible electrochemical doping of the electrochromic polymer whichresults in great colour changes, for example from colourless to blue.The assembly is driven by means of defined voltages.

The reduction and oxidation processes in the electrochromic assembly ofthe invention generally occur by electron uptake and release at thecathode and anode, respectively, and the potential difference betweenthe electrodes is preferably from 0.1 to 5 V, very particularlypreferably from 0.1 to 3 V. After the electric potential is switchedoff, the previously achieved coloration can be maintained for some time(memory effect) so that permanent coloration can be achieved withminimum energy consumption. Charge equilibration and thus decolorationcan be achieved by brief reversal of the polarity.

The light-stabilized electrochromic assembly of the invention can besupplied with power by means of solar modules, even in the case ofrelatively large areas.

To improve wetting of the substrates, it is also possible to add awetting agent (e.g. Fluortensid)

EXAMPLES Example 1

Application of an electrochromic polymer to a conductive substrate

The polymer Baytron® P (aqueous dispersion of the conductive polymerPEDT/PSS, polyethylenedioxythiophene-polystyrenesulphonate from BayerAG) ##STR5## is applied from aqueous solution additionally containingisopropanol to the electrically conductive side of a K-glass plate(heat-protection glass from Flachglas, surface resistance ˜20 Ω/sq) bymeans of a spin coater, with four applications of 15 seconds each beingmade at a rotational speed of 1500 rpm. During application, the solventis evaporated by means of a hair dryer.

This gives a transparent, only very slightly bluish polymer film.Measurement of the layer thickness by means of a profilometer gave avalue of 0.6 μm.

Example 2

Preparation of an ion-storage layer TiO₂ --CeO₂)

0.548 g of cerium ammonium nitrate (Ce(NH₄)₂ (NO₃)₆) together with 100ml of dry ethanol is placed in a reaction vessel and admixed with 0.142g of titanium isopropoxide. This solution is stirred for a number ofhours at room temperature. The sol obtained in this way is subsequentlyapplied by spin coating at 1500 rpm to the conductive side of a K-glassplate (time: 10 sec).

This layer is heated at 200° C. for 1 hour, giving an ion-storage layerof TiO₂ --CeO₂ (1:2).

Example 3

Preparation of a UV-stabilized gel electrolyte

7.6 g of the photocrosslinkable acrylate V531-2,6 (Bayer AG) are mixedwith 0.19 g (2.5% by weight) of photoinitiator ®Darocure 1173 fromMerck, Darmstadt, 0.3 g (3% by weight) of lithiumtrifluoromethanesulphonate from Aldrich and 0.1 g (1% by weight) of4-methacryl-2-hydroxybenzophenone (Poly-Science) in 2 g of dry1,2-propylene carbonate from Aldrich. This mixture is pourable and canbe crosslinked photochemically, by means of which a gel electrolytewhich no longer flows can be prepared. In this way, the UV absorber4-methacryl-2-hydroxybenzophenone is immobilized in the V531-2,6 matrix.

Example 4

Manufacture of a complete electrochromic cell with a crosslinked gelelectrolyte containing UV absorber

The still uncrosslinked gel electrolyte from Example 3 is applied in awet film thickness of 200 μm to the ion-storage layer from Example 2 andbrought into contact with an electrochromic layer from Example 1. Thiscomposite is conveyed at a belt speed of 7.5 n/min under a UV lamp (ISTlamp). This crosslinks the gel electrolyte and gives transparent systemscontaining a gel electrolyte which no longer flows.

Example 5

Function test of the UV-stabilized cell

The function of the UV-stabilized electrochromic cell of Example 4 istested by application of a potential of 2.5 V from a DC source.

Reversal of the polarity enables both states (coloured/decoloured) to bedemonstrated.

The coloured state has an intense blue coloration. Repeated reversal ofthe polarity enables the stability of the electrochromic assembly to beshown (c.f. FIG. 2).

Example 6

Manufacture of an electrochromic cell without UV absorber

For comparison with a cell without UV protection, a gel electrolyteidentical to the gel electrolyte from Example 3 except for the absenceof a UV absorber was prepared.

The complete electrochromic cell was manufactured as described inExample 4.

Example 7

Function test of the cell without UV absorber

This was carried out by a method analogous to Example 5. No differencein the switching behaviour of the UV-stabilized cell can be observedvisually.

Example 8

Illumination of the cells in the Xenotest

To determine the effect of the UV absorber, the electrochromic cells(with and without UV absorber, respectively) are irradiated for one weekin an illumination apparatus Xenotest 150 S from Heraeus. Theirradiation power in the "outdoor sunlight" configuration used is 1570W/m².

Example 9

Comparison of the electrochromic cells

Comparison of the electrochromic cells (with and without UV absorber,respectively) by a method analogous to Example 5 shows that, afterirradiation, the electrochromic cell which had not been UV-stabilizeddisplays significantly poorer properties in respect of the switchingbehaviour and the maximum achievable coloration.

What is claimed is:
 1. A UV-stabilized electrochromic assembly having aUV-stabilized gel electrolyte comprising an immobilized UV absorber in alayer structure, wherein one layer is an electrically conductiveelectrochromic polydioxythiophene and a further ion-storage layer is oneor more ion-storage compounds selected from the group consisting ofcompounds having the formulas

    ______________________________________                                        Me.sup.1 O.sub.2,     (I)                                                     Me.sup.2.sub.2 O.sub.5,                                                                             (II)                                                    Li.sub.x Me.sup.1 O.sub.2,                                                                          (III)                                                   Li.sub.x Me.sup.2.sub.2 O.sub.5,                                                                    (IV)                                                    Li.sub.x Me.sup.1 O.sub.2+x/2,                                                                      (V)                                                     Li.sub.x Me.sup.2.sub.2 O.sub.5+x/2,                                                                (VI)                                                    Me.sup.3 O,           (VII)                                                   Me.sup.3 O.sub.x,     (VIII)                                                  M.sub.x Me.sup.3 O,   (IX)                                                    M.sub.x Me.sup.3 O.sub.2,                                                                           (X)                                                     M.sub.x Me.sup.3 O.sub.y,                                                                           (XI)                                                    Me.sup.4 O.sub.3,     (XII)                                                   M.sub.x Me.sup.4 O.sub.3,                                                                           (XIII)                                                  M.sub.x Me.sup.4.sub.(1-x) Me.sup.4.sub.x O.sub.3,                                                  (XIV)                                                   Me.sup.3 (OH).sub.2,  (XV)                                                    Me.sup.3 O(OH),       (XVI)                                                   MMe.sup.3 O.sub.2,    (XVII)                                                  Me.sup.3 O.sub.2,     (XVIII)                                                 Me.sup.3.sub.2 O.sub.3,                                                                             (XIX)                                                   Me.sup.3.sub.2 O.sub.3.H.sub.2 O, and                                                               (XX)                                                    LiMe.sup.5 O.sub.3,   (XXI)                                                   ______________________________________                                    

wherein Me¹ and Me² each represent a metal of transition group III, IV,or V of the Mendeleev Periodic Table, Me³ and Me⁴ each represent a metalof transition group VI or VIII of the Mendeleev Periodic Table, Me⁵represents a metal of transition group V of the Mendeleev PeriodicTable, x represents a number from 0.001 to 5, y represents a number from0.001 to 5, and M represents a metal of main group I of the MendeleevPeriodic Table or a proton.
 2. A UV-stabilized electrochromic assemblyaccording to claim 1 whereinMe¹ represents zirconium, cerium, ortitanium, Me² represents vanadium, or niobium, Me³ represents nickel oriridium, Me⁴ represents molybdenum or tungsten, and Me⁵ representsvanadium, niobium, or tantalum.
 3. A UV-stabilized electrochromicassembly according to claim 1 wherein the ion-storage layer is one ormore ion-storage compounds selected from the group consisting ofcompounds having the formulas

    V.sub.2 O,

    Li.sub.X V.sub.2 O.sub.5,

    Li.sub.X V.sub.2 O.sub.5+X/2,

    CeO.sub.2,

    Li.sub.X CeO.sub.2,

    Li.sub.X CeO.sub.2+X/2,

    Nb.sub.2 O.sub.5,

    Li.sub.x Nb.sub.2 O.sub.5,

    Li.sub.x Nb.sub.2 O.sub.5+x/2,

    LiNbO.sub.3,

    NiO,

    NiO.sub.2,

    Ni(OH).sub.2,

    NiO(OH),

    LiNiO.sub.2,

    Ni.sub.2 O.sub.3,

    Ni.sub.2 O.sub.3.H.sub.2 O,

    Li.sub.x NiO, and

    WO.sub.3.


4. 4. A UV-stabilized electrochromic assembly according to claim 1wherein the ion-storage layer is

    TiO.sub.2 --CeO.sub.2,

    CeO.sub.2 --V.sub.2 O.sub.5,

    TiO.sub.2 --V.sub.2 O.sub.5,

    Li.sub.x CeO.sub.2 --Li.sub.x V.sub.2 O.sub.5,

    Li.sub.x TiO.sub.2 --Li.sub.x V.sub.2 O.sub.5,

    Li.sub.x TiO.sub.2 --Li.sub.x CeO.sub.2,

    V.sub.2 O.sub.5 --Nb.sub.2 O.sub.5,

    Li.sub.x V.sub.2 O.sub.5 --Li.sub.x Nb.sub.2 O.sub.5,

    NiO--CeO.sub.2, or

    NiO--TiO.sub.2 --TiO.sub.2.


5. A UV-stabilized electrochromic assembly according to claim 1 whereinthe electrically conductive electrochromic polydioxythiophene comprisesstructural units of the formula (XXII) ##STR6## wherein A¹ and A²represent, independently of one another, substituted or unsubstituted(C₁ -C₄)-alkyl or together form substituted or unsubstituted (C₁-C₄)-alkylene, andn represents an integer from 2 to 10,000, andpolyanion counterions.
 6. A UV-stabilized electrochromic assemblyaccording to claim 1 wherein the electrically conductive electrochromicpolydioxythiophene comprises structural units of the formulas ##STR7##wherein R₁ and R₂ represent, independently of one another, hydrogen or asubstituted or unsubstituted (C₁ -C₁₈)-alkyl, (C₂ -C₁₂)-alkenyl, (C₃-C₇)-cycloalkyl, (C₇ -C₅)-aralkyl, (C₆ -C₁₀)-aryl, (C₁ -C₁₈)-alkyloxy,or (C₂ -C₁₈)-alkyloxy ester group,R₃ and R₄ represent, independently ofone another, hydrogen or a (C₁ -C₁₈)-alkyl, (C₂ -C₁₂)-alkenyl, (C₃-C₇)-cycloalkyl, (C₇ -C₁₅)-aralkyl, (C₆ -C₁₀)-aryl, (C₁ -C₁₈)-alkyloxy,or (C₂ -C₁₈)-alkyloxy ester group substituted by at least one sulphonategroup, with the proviso that R₃ and R₄ cannot both be hydrogen, and nrepresents an integer from 2 to 10,000, and polyanion counterions.
 7. AUV-stabilized electrochromic assembly according to claim 6 whereinpolyanion counterions are anions of polymeric carboxylic acid and/orpolymeric sulphonic acids.
 8. A UV-stabilized electrochromic assemblyaccording to claim 1 wherein the electrically conductive electrochromicpolydioxythiophene comprises structural units of the formulas ##STR8##wherein R₃ represents hydrogen or a (C₁ -C₁₈)-alkyl, (C₂ -C₁₂)-alkenyl,(C₃ -C₇)-cycloalkyl, (C₇ -C₁₅)-aralkyl, (C₆ -C₁₀)-aryl, (C₁-C₁₈)-alkyloxy, or (C₂ -C₁₈)-alkyloxy ester group substituted by atleast one sulphonate group, andn represents an integer from 2 to 10,000,and polyanion counterions.
 9. A UV-stabilized electrochromic assemblyaccording to claim 8 wherein polyanion counterions are anions ofpolymeric carboxylic acid and/or polymeric sulphonic acids.
 10. AUV-stabilized electrochromic assembly according to claim 1 wherein theelectrochromic assembly contains at least one transparent electricallyconductive coating on a substrate.
 11. A UV-stabilized electrochromicassembly according to claim 1 wherein an electrically conductivepolydioxythiophene is a conductive electrode material.
 12. AUV-stabilized electrochromic assembly according to claim 1 wherein aplate (substrate) which has been mirrored by means of a metal is used asa conductive layer for connection to a power source.
 13. A UV-stabilizedelectrochromic assembly according to claim 1 additionally comprising atransparent crosslinked gel electrolyte layer containing a crosslinkedpolymer, a lithium salt, a solvent or solvent mixture, and one or morelight stabilizers that are chemically incorporated into the crosslinkedgel electrolyte layer.
 14. A UV-stabilized electrochromic assemblyaccording to claim 13 wherein the polymer is a photocrosslinkablepolymer.
 15. A UV-stabilized electrochromic assembly according to claim13 wherein the gel electrolyte contains light stabilizers and organicand/or inorganic fillers and/or additives.
 16. A UV-stabilizedelectrochromic assembly according to claim 1 wherein the UV absorber isselected from the group consisting of benzophenones, benzotriazoles,organonickel compounds, salicylic esters, cinnamic esters, benzylidenemalonates, benzoic esters, oxalanilides, stearically hindered amines,polymeric sterically hindered amines, and mixtures thereof and ischemically bound to the gel electrolyte.